In a field experience dating from July, 1874, in nearly every known vertebrate horizon of North America, I know of no beds so difficult of exploitation as those of the Permian of northern Texas. As a rule the vertebrate fossils are found more or less broken and weathered, scattered about on the sloping exposed surfaces. Occurring as the bones do, almost invariably concealed beneath a thin or thick covering of cemented matrix, so like the color and form of the countless millions of nodules, it is only when they have been broken up and weathered by exposure that the slight colorational differences presented by the fractured surfaces distinguish them. It thus happens that by far the larger part of the material secured, especially that of the smaller animals, is more or less fragmentary in character, though fortunately preserved from rapid disintegration . . .